Orthogonal sequences have been used for shared use of communication capabilities that may not be entirely divided in time or frequency. In theory, the orthogonal properties of the sequences for modulating the communication signals enable the signals to co-exist with manageable interference between the signals.
“Remaining issues on PHICH indexing and PHICH to RE mapping” issued by LG Electronics to 3GPP TSG RAN WG1 #52 discloses PHICH mapping where PHICHs are mapped in I channel first, and then remaining PHICHs are mapped in Q channel.
However, due to imperfections in hardware, synchronisation, or communication channels, interference beyond what is manageable by the design of a telecommunication system may occur. It is therefore a desire to at least alleviate such effects.